Heretofore, video tape recorders combined with cameras are arranged to record video data that have been produced by imaging a desired subject on a recording medium which includes a magnetic tape. In recent years, various recording apparatus using disk-shaped recording mediums such as hard disks or the like have been proposed as a replacement for magnetic tapes.
There have been available various interfaces that are widely used in information processing apparatus such as computers or the like. It has been considered that recording and reproducing apparatus which incorporate disk-shaped recording mediums such as hard disks or the like may be simply constructed by using such existing interfaces. Using those interfaces, recording and reproducing apparatus can be simply constructed so as to be able to input and output video data to and from personal computers, thus allowing the recording and reproducing apparatus to find an increased range of applications.
With the recording and reproducing apparatus being thus arranged, however, a large-capacity buffer memory needs to be provided for the transfer of data to the recording and reproducing apparatus.
FIG. 1 of the accompanying drawings is a block diagram showing a flow of video data in a recording apparatus for recording video data. In order to achieve a sufficient level of image quality based on video data that are compressed by MPEG (Moving Picture Experts Group), it is necessary to transfer the video data at a rate of about 10 [Mbps]. In the arrangement shown, an encoder 2 outputs video data as streaming data at the rate of about 10 [Mbps].
A disk-shaped recording medium such as a hard disk or the like records the video data intermittently thereon at a data transfer rate that is about twice the data transfer rate of the video data output from the encoder 2 because the recording medium 3 needs various processing modes including a rotation waiting mode, a seeking mode, and a retrying mode. Therefore, when video data are output as streaming data at the rate of 10 [Mbps] from the encoder 2, the video data are transferred to the recording medium 3 at a data transfer rate of 20 [Mbps] at maximum.
The video data are transferred to and from a personal computer (PC) 4 through an interface (I/F) 5 according to IEEE (The Institute of Electrical and Electronics Engineers, Inc.) 1394 or USB (Universal Serial Bus), and transferred to and from a recording and reproducing apparatus which uses the recording medium 3 through an interface which includes an ATAPI (AT Attachment Packet Interface) for performing a trouble-free data exchange with the interface according to IEEE 1394. The recording and reproducing apparatus which uses the recording medium 3 requires a buffer memory having a capacity of about 4 [Mbytes] in order to reduce the frequency of data transfer to and from the personal computer 4 connected by the interface 5 for thereby preventing the processing efficiency of the personal computer 4 from being lowered. The ATAPI interface has a data transfer rate of 100 [Mbps].
When video data output from the encoder 2 are recorded on the recording medium 3, the amount of transferred data varies as shown in FIG. 2 of the accompanying drawings in a system buffer 6 that is connected to the encoder 2 and the ATAPI interface and a drive buffer 7 that is connected to the recording medium 3. In FIG. 2, the data output from the encoder 2, the data output from the system buffer 6, and the data output to the recording medium 3 are represented D1, D2, D3, respectively. In FIG. 2, the assembly is in an ideal state where the rotation waiting mode and other modes are ignored in the recording and reproducing apparatus.
When video data start to be recorded (REC Start), compressed video data D1 are output as streaming data at 10 [Mbps] from the encoder 2 ((A) in FIG. 2). The system buffer 6 and the drive buffer 7 accumulate the video data D1 and intermittently outputs the accumulated video data D1 ((B) to (E) in FIG. 2). Specifically, when the video data have been accumulated to a predetermined amount in the system buffer 6 (at time t1), the data accumulated in the system buffer 6 are transferred to the drive buffer 7 at 100 [Mbps] (in a period from time t1 to time t2), which start recording the data on the recording medium 3 at 20 [Mbps].
When the amount of data accumulated in the system buffer 6 and the drive buffer 7 are reduced to a certain level, then the system buffer 6 and the drive buffer 7 stop sending out the data. This processing sequence will subsequently be repeated.
If the drive buffer 7 has a storage capacity of 4 [Mbytes], then since the drive buffer 7 outputs the video data that are input thereto at the data transfer rate of 100 [Mbps] to the recording medium 3 at the data transfer rate of 20 [Mbps], the data transfer rate at which the video data are input to the drive buffer 7 is greater than the data transfer rate at which the video data are output from the drive buffer 7, and hence the video data are progressively accumulated in the drive buffer 7. Specifically, in 0.5 [sec.] from time t1, the video data are accumulated in the drive buffer 7 to the amount of 4 [Mbytes], whereupon no empty storage area is available in the drive buffer 7. At this time, the system buffer 6 needs to stop outputting the video data.
After the video data have started to be recorded until the system buffer 6 stops inputting the video data to the drive buffer 7, the system buffer 6 has recorded 5 [Mbytes] of video data at maximum. Therefore, if it is assumed that the overall assembly operates in an ideal condition, then the system buffer 6 is required to have a storage capacity of at least 5 [Mbytes].
FIG. 3 of the accompanying drawings shows a situation in which an error has occurred while video data are being recorded on the recording medium 3, and the video data stored in the system buffer 6 is to be re-transmitted. Since the system buffer 6 has to store the video data to be re-transmitted, the system buffer 6 requires a large storage capacity. In the example shown in FIG. 3, the video data sent from time t1 to time t2 are retried at time t3 or later, and the system buffer 6 needs to have a storage capacity of 9 [Mbytes].
Therefore, if the large-capacity drive buffer is employed so as to be able to input data to and output data from the computer for increased affinity with the computer, the buffer memory (system memory) for supplying streaming data to the drive buffer is required to have a storage capacity that is several times greater than the storage capacity of the drive buffer.